A conventional water-cooled engine, such as used in a remote controlled boat and shown in FIG. 1, includes a water pumping mechanism 1 attached to the engine to take in water from the rear of the boat and pump same into the interior of the engine to cool same. The spent cooling water is then pumped out of the engine and drained from the boat together with the engine exhaust gas through a discharge mechanism 2. However, discharge mechanism 2 is of a single pipe design and must simultaneously discharge both the exhaust gas and spent cooling water through the single pipe during use. The single pipe configuration causes the exhaust gas and spent cooling water to constantly impact upon each other, undergo undesirable mixing within mechanism 2, require an increase in energy consumption and result in reduction in engine performance.